1. Technical Field
This invention relates in general to sealing motors and in particular to a ferrofluid cap seal for a hard disk drive spindle motor.
2. Background Art
Referring to FIG. 1, a schematic drawing of an information storage system comprising a magnetic hard disk drive 11 is shown. Drive 11 has a base 13 containing a plurality of stacked, parallel magnetic disks 15 (one shown) which are closely spaced apart. Disks 15 are rotated by a spindle motor (not shown) located therebelow about a central drive hub 17. An actuator 21 is pivotally mounted to base 13 about a pivot assembly 23. A controller 19 is mounted to base 13 for selectively moving actuator 21 as will be described below.
Actuator 21 has a mounting support 25, a pair of parallel, cantilevered load beams or suspensions 27 extending from mounting support 25, and a head gimbal assembly 29 having at least one magnetic read/write head secured to each suspension 27 for magnetically reading data from or magnetically writing data to disks 15. Suspensions 27 have a spring-like quality which biases or maintains them in parallel relationship relative to one another. A motor assembly 31 having a conventional voice coil motor is also mounted to pivot assembly 23 opposite head gimbal assemblies 29. Movement of actuator 21 (indicated by arrows) moves head gimbal assemblies 29 radially across tracks on the disks 15 until the heads on assemblies 29 settle on the target tracks.
The spindle motor contains bearings that incidentally emit very small amounts of oil vapor and aerosol droplets of grease. These are potential sources of contamination in the disk drive. Some prior art disk drive use ferrofluid seals to seal the bearings. Ferrofluid seals are practically impermeable to emissions from bearings and function by suspending magnetically attracted fluid across an opening. The suspended fluid, which is essentially frictionless, forms an effective liquid seal.
Some prior art ferrofluid seals allow a very small amount of ferrofluid to migrate into the disk drive over time. In addition, a ferrofluid droplet may be inadvertently dispensed onto the top of the seal assembly, or excess ferrofluid may be dispensed into the seal. Such leakage and excess can cause contamination of the drive leading to data loss or even catastrophic failure of the drive. In the prior art, ferrofluid caps have been used to seal ferrofluid seals. Techniques for securing the caps in the spindle motor have included adhesive bonding and mechanical snap fits. The mechanical snap fit, annular caps were provided with slits and a lip around their outer perimeter to enable them to be snapped over the backiron of the spindle motor. The snap fit caps were designed to protect the ferrofluid seal while handling during manufacturing. Unfortunately, the bonding and the subsequent inspection process are expensive, and the snap fit cap designs provide no protection against ferrofluid escape. Thus, an improved cap for preventing the escape of ferrofluid from ferrofluid seals is needed.
A hard disk drive spindle motor has a hub, a drive shaft, and a bearing therebetween. The spindle motor also has a ferrofluid seal to prevent any incidental oil emissions from the bearing from entering the drive. A ferrofluid cap is mounted on the axial end of the spindle motor for sealing the ferrofluid seal. The cap is a flat ring and has an elastomeric pad around its outer edge. The pad seats in a recess in the bore of the hub. The cap does not touch the shaft as it rotates with the hub about the shaft. Any excess ferrofluid from the ferrofluid seal is forced radially outward away from the shaft by centrifugal force. The cap contains the excess ferrofluid within the spindle motor and prevents it from entering other areas of the disk drive.